This invention relates to apparatus for forming a crystalline ribbon and, more particularly, to a bellows arrangement used with such apparatus.
A particular technique for growing crystalline ribbons from a pool of liquid, commonly referred to as a melt, is the EFG technique (Edge-defined Film-fed Growth). In carrying out an EFG technique, there is provided a furnace containing heating means and a crucible in which raw material is heated to form the melt. The crucible, in turn, contains a die including a capillary passage formed with growth control surfaces at its upper edge. The melt flows up the capillary and rests on the growth control surfaces. This furnace is airtight and usually purged with an inert gas such as argon so that there is no contaminating moisture or gases therein. Such contaminants can cause the formation of unacceptable microvoids in the ribbon. There is also provided a seed crystal carried by slider means which is lowered into contact with the melt at the top of the growth control surfaces whereupon, because of the temperature gradient between the liquid and the seed, a crystalline ribbon is epitaxially grown on the seed as a continuation thereof. By pulling the seed away from the growth control surfaces at an appropriate rate, an elongated ribbon is formed.
Ribbons up to 7 feet (approximately 213 cm) in length have been grown with this technique. To accommodate the ribbon, it is usual to provide an airtight bellows between the furnace and the slider means so that contaminating moisture and gases do not enter the growing chamber of the furnace. However, the bellows may contain fine pores and/or small puncture openings that allow contaminants to enter the interior thereof and flow to the growth chamber of the furnace. When this happens, the unacceptable microvoids can be formed in the ribbon. Moreover, a lint type material collects in the growth chamber of the furnace requiring its frequent disassembly and cleaning.